全文获取类型
收费全文 | 258篇 |
免费 | 9篇 |
专业分类
化学 | 186篇 |
晶体学 | 8篇 |
力学 | 13篇 |
数学 | 28篇 |
物理学 | 32篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 3篇 |
2020年 | 3篇 |
2019年 | 5篇 |
2017年 | 3篇 |
2016年 | 9篇 |
2015年 | 6篇 |
2014年 | 5篇 |
2013年 | 16篇 |
2012年 | 14篇 |
2011年 | 15篇 |
2010年 | 11篇 |
2009年 | 7篇 |
2008年 | 7篇 |
2007年 | 24篇 |
2006年 | 16篇 |
2005年 | 11篇 |
2004年 | 11篇 |
2003年 | 6篇 |
2002年 | 10篇 |
2001年 | 10篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1997年 | 4篇 |
1996年 | 5篇 |
1995年 | 2篇 |
1994年 | 4篇 |
1993年 | 1篇 |
1992年 | 8篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1973年 | 2篇 |
1959年 | 2篇 |
1958年 | 5篇 |
排序方式: 共有267条查询结果,搜索用时 15 毫秒
71.
Takehiro Kohara Yukihiko Hashimoto Rieko Shioya Kazuhiko Saigo 《Tetrahedron: Asymmetry》1999,10(24):485-4840
1-Mesitylethylamine was designed as a new non-natural chiral auxiliary. Racemic 1-mesitylethylamine could be synthesized in two steps from mesityl cyanide and could be resolved via separation of diastereomeric carbamates derived from (−)-menthyl chloroformate, followed by reduction with DIBAL and acidic hydrolysis. Imines, prepared from enantiopure 1-mesitylethylamine and aromatic aldehydes, reacted with Danishefsky’s diene in the presence of a Lewis acid to give cycloaddition products, 4-pyridone derivatives, with high diastereoselectivity. 相似文献
72.
Two bacteria exhibiting resistance to toxic arsenic were isolated. These had been contaminated with arsenic in a Chlorella sp. culture medium containing arsenic. The two bacteria were identified as Klebsiella oxytoca and Xanthomonas sp., and grew well in a peptone medium at neutral pH at 30°C, reaching the stationary phase in ca 100h and 70h, respectively. The growth of the bacteria was not affected by arsenic(V) concentrations in the medium as high as 1000mg dm?3. The bacteria bioaccumulated arsenic, a part of the arsenic being methylated. The bioaccumulation exhibited its peak around the turing point from the log phase to the stationary phase. The relative content of methylated arsenic in the excrement was greater than that in the bacterial cells. Adaptation treatment of inorganic arsenic caused an increase in the bioaccumulation of inorganic arsenic by K. oxytoca. Such a situation was not observed in the case of Xanthomonas sp. The bacteria also bioaccumulated methylated arsenic compounds, and demethylation of these species was observed. When the bacteria were killed by ethanol, arsenic was not taken up by the cells. 相似文献
73.
Tadamasa Nemoto Kensuke Naka Yoshiki Chujo 《Journal of polymer science. Part A, Polymer chemistry》2008,46(8):2864-2868
To study the bidentate coordination effect on the polycondensation of L ‐valinates between metal triflates as a Lewis acid and methoxy groups, we carried out the polycondensation of 2‐methoxy‐4‐nitrophenyl L ‐valinate ( 1a ) and 2‐methoxyphenyl L ‐valinate ( 1b ) in the presence of the various kinds of rare‐earth triflates in DMF solution at room temperature. The polymerizations of 1a did not proceed without any metal triflates. In the presence of 5 mol% triflates, especially Sc(OTf)3, the polymerization proceeded effectively. After the reaction mixture was poured into water, the product was collected, which was recognized as poly(L ‐valine)s by FTIR spectrum and GPC measurement. The yield of the product from the polymerization of 1a with Sc(OTf)3 was higher than that from the polymerization of 4‐nitrophenyl L ‐valinate ( 1c ) with Sc(OTf)3. This result indicates that the polymerization of 1a was promoted to introduce the methoxy group on the o‐position of the phenyl ring at the ester group with the aim of the bidentate coordination effect between metal triflates and L ‐valinate. As a control experiment, we carried out the polycondensation of 1b in the presence of 5 mol% metal triflates; however, any polymerization did not proceeded. That reason is from the lower activity of activated L ‐valinate ( 1b ). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2864–2868, 2008 相似文献
74.
Tahereh Mousavand Jing Zhang Satoshi Ohara Mitsuo Umetsu Takashi Naka Tadafumi Adschiri 《Journal of nanoparticle research》2007,9(6):1067-1071
Titanium oxide (TiO2) nanocyrstals which are perfectly dispersed in organic solvents are synthesized by organic-ligand-assisted supercritical
hydrothermal synthesis. The addition of hexaldehyde to the supercritical hydrothermal synthesis of TiO2 leads to the in-situ surface modification, which enables the synthsized TiO2 nanocrystals to be perfectly dispersed in iso-octane because of its hydrophobic nature. Further, the one-pot synthesis of
hybrid materials results in the significant reduction of the particles size, probably due to the capping effect of hexaldehyde
to suppress the particles growth. 相似文献
75.
Kensuke Naka Tadamasa Nemoto Yoshiki Chujo 《Journal of polymer science. Part A, Polymer chemistry》2003,41(10):1504-1510
We describe a novel method of polymerization, via the insertion of activated glycine esters into N‐salicylideneglycinato‐aquo‐copper(II) chelate ( 1 ), that uses the reactivity of the metal chelate. In the absence of 1 , a high molecular weight polyglycine was formed as a white precipitate after triethylamine was added to an N,N‐dimethylformamide solution of 4‐nitrophenyl glycinate ( 3a ). In the presence of 5 mol % 1 , however, the polymerization proceeded homogeneously. After the reaction mixture was poured into tetrahydrofuran, a condensation product of glycine was obtained. According to gel permeation chromatography analysis, the product consisted of high and low molecular weight fractions. The former and latter were obtained by self‐polycondensation and polycondensation via the insertion of 3a into 1 , respectively. So that the self‐polycondensation of activated glycinates would be depressed, 2‐chlorophenyl ( 3b ), 3‐chlorophenyl ( 3c ), 4‐chlorophenyl, and phenyl glycinates were used as less activated glycine esters. For the polymerization of 3b and 3c , the polymerization via the insertion of activated glycinates into 1 was promoted. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1504–1510, 2003 相似文献
76.
Yukihiko Namikawa 《Mathematische Annalen》1976,221(3):201-241
This is a continuation of the article with the same title appeared in this journal, to the introduction of which we referr the reader for the summary of contents of this article.Dedicated to Professor K. Kodaira on his 60th birthday. 相似文献
77.
78.
P. Estrela A. de Visser T. Naka F.R. de Boer L.C.J. Pereira 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(4):449-454
The effect of hydrostatic pressure ( p
? 1.8 GPa) on the non-Fermi liquid state of U2Pt2In is investigated by electrical resistivity measurements in the temperature interval 0.3-300 K. The experiments were carried
out on single-crystals with the current along (
I
||
c
) and perpendicular (
I
||
a
) to the tetragonal axis. The pressure effect is strongly current-direction dependent. For I
||
a we observe a rapid recovery of the Fermi-liquid T2-term with pressure. A comparison of the data with the magnetotransport theory of Rosch provides evidence for the location
of U2Pt2In at an antiferromagnetic quantum critical point. For I
||
c the resistivity increases under pressure, indicating the enhancement of an additional scattering mechanism.
Received 2 March 2001 and Received in final form 29 June 2001 相似文献
79.
Yasuhisa Kohara Keiji Kubo Eiko Imamiya Takehiko Naka 《Journal of heterocyclic chemistry》2000,37(6):1419-1423
The reaction of amidoximes 1 with 1,1′‐thiocarbonyldiimidazole (TCDI) followed by treatment with silica gel or boron trifluoride diethyl etherate (BF3·OEt2) provided 3‐substituted 4,5‐dihydro‐5‐oxo‐1,2,4‐thiadiazoles 2 in moderate yields. The Lewis acids are considered to promote the rearrangement of the thioxocarbamate intermediates 5 to the thiol carbarn ate intermediates 7 , which cyclize to afford 4,5‐dihydro‐5‐oxo‐1,2,4‐thiadiazoles 2 . 相似文献
80.